Effects of chain branching and chirality on liquid crystalline phases of bent-core molecules: blue phases, de Vries transitions and switching of diastereomeric states

Ocak, Hale; Bilgin‐Eran, Belkız; Prehm, Marko; Schymura, Stefan; Lagerwall, Jan P. F.; Tschierske, Carsten

doi:10.1039/c1sm05826f

Cited by 70 publications

(54 citation statements)

References 80 publications

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“…The details of the synthetic scheme were reported elsewhere (compound ( S )‐4 in Ref. ). As observed and reported by DSC and polarizing microscopy, T4 exhibits a phase sequence Cr 1 54 Cr 2 80 (M 1 42 BPIII 58) Iso in which BPIII is monotropic and M 1 is a mesophase with unknown structure.…”

Section: Figurementioning

confidence: 99%

“… a) Chemical structure of the BPIII compound T4 used in the present work . b) Textures at 52.5 °C before and after the application of an electric field E =9 V μm −1 (1 kHz).…”

Section: Figurementioning

confidence: 99%

“…To compare, we have studied the dielectric property of the racemic form of T4 (compound rac ‐4 in Ref. ), which exhibits a N phase instead of the BPIII. Due to the fact that a perfect homeotropic alignment of bent‐core director could hardly be obtained for dielectric study, we prepared a mixture of 5.9 mol % of rac ‐4 and a rod‐like nematic 5CB (4‐pentyl‐4′‐cyanobiphenyl) and compared the dielectric anisotropy of the mixture with that of another mixture which was composed of exactly 5.9 mol % of M12 and 5CB .…”

Section: Figurementioning

confidence: 99%

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Unusual Electro‐Optic Kerr Response in a Self‐Stabilized Amorphous Blue Phase with Nanoscale Smectic Clusters

Hafuri

Ocak

et al. 2016

ChemPhysChem

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We investigated the electro-optic response in the "foggy" amorphous blue phase (BPIII) as well as in the isotropic phase. To the best of our knowledge, such a study has not yet been performed due to the very limited thermal range of BPIII. In this study, we used a single-component chiral bent-core liquid crystal with a self-stabilized BPIII, which is stable over a wide temperature range. The results show that the response time is on the order of hundreds of microseconds in the isotropic phase and increases to 1-2 ms in the BPIII (at TI-BP -T <1), then drastically increases up to a few tens of milliseconds upon further cooling in BPIII. Such an unusual behavior was explained on the basis of the high rotational viscosity and/or the existence of nanoscale smectic (Sm) clusters. The Kerr constant was also measured and found to be ∼500 pm V(-2) , which is the largest among bent-core BP systems reported so far and comparable with that of polymer-stabilized BPs.

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Section: Figurementioning

confidence: 99%

“… a) Chemical structure of the BPIII compound T4 used in the present work . b) Textures at 52.5 °C before and after the application of an electric field E =9 V μm −1 (1 kHz).…”

Section: Figurementioning

confidence: 99%

Section: Figurementioning

confidence: 99%

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Unusual Electro‐Optic Kerr Response in a Self‐Stabilized Amorphous Blue Phase with Nanoscale Smectic Clusters

Hafuri

Ocak

et al. 2016

ChemPhysChem

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“…In recent years, the investigation of molecules having intermediate structures between those of the typical bent‐core molecules and linear rodlike molecules has received significant attention, as this provides new phase structures and phenomena . One class of compounds with reduced molecular bend are acylated 4‐cyanoresorcinols, for which numerous unusual LC phases were reported . The polar cyano group is known to affect the conformation of the adjacent carboxyl group by dipole coupling with the C=O group, which favors helical molecular conformations and reduces the molecular bend by increasing the angle α (see Figure ) from 120 to 130–140° .…”

Section: Introductionmentioning

confidence: 99%

Polar Order and Symmetry Breaking at the Boundary between Bent‐Core and Rodlike Molecular Forms: When 4‐Cyanoresorcinol Meets the Carbosilane End Group

Westphal

Gallardo

Caramori

et al. 2016

Chemistry A European J

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Two isomeric achiral bent-core liquid crystals involving a 4-cyanoresorcinol core and containing a carbosilane unit as nanosegregating segment were synthesized and were shown to form ferroelectric liquid-crystalline phases. Inversion of the direction of one of the COO groups in these molecules leads to a distinct distribution of the electrostatic potential along the surface of the molecule and to a strong change of the molecular dipole moments. Thus, a distinct degree of segregation of the carbosilane units and consequent modification of the phase structure and coherence length of polar order result. For the compound with larger dipole moment (CN1) segregation of the carbosilane units is suppressed, and this compound forms paraelectric SmA and SmC phases; polar order is only achieved after transition to a new LC phase, namely, the ferroelectric leaning phase (SmCLs PS ) with the unique feature that tilt direction and polar direction coincide. The isomeric compound CN2 with a smaller dipole moment forms separate layers of the carbosilane groups and shows a randomized polar SmA phase (SmAPAR ) and ferroelectric polydomain SmCs PS phases with orthogonal combination of tilt and polar direction and much higher polarizations. Thus, surprisingly, the compound with the smaller molecular dipole moment shows increased polar order in the LC phases. Besides ferroelectricity, mirror-symmetry breaking with formation of a conglomerate of macroscopic chiral domains was observed in one of the SmC phases of CN1. These investigations contribute to the general understanding of the development of polar order and chirality in soft matter.

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“…[29] On the other hand, the use of branched chains to modify the thermal properties of a single-component system has been well documented. [30] Recently, the contribution of terminal branched chains in the racemic and chiral form on the BP was reported by Hale et al [31] A comprehensive literature search revealed that any cholesterol derivative having the combination of electronegative fluorine atom with branched chain in the benzoate part is not known in the literature. In order to study the effects of these substitutions, we prepared a series of cholesteryl benzoates with branched saturated/ unsaturated chain and lateral fluorine substitution.…”

Section: Introductionmentioning

confidence: 99%

Effects of chain branching and lateral fluorine substitution on mesomorphism of cholesteryl benzoates

2014

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The mesogenic cholesteryl 4′-alkoxyphenyl-4-carboxylates possessing terminal normal/branched/saturated/unsaturated alkyl chains with laterally ortho/meta substituted electronegative fluorine atom are described. All the homologues exhibited enantiotropic mesomorphism. Smectic A phase, chiral nematic, blue phase (BP) and TGB A phases were observed in different homologues. All the novel compounds were characterised by spectroscopic and elemental analysis. Thermal investigations and mesophase characterisations for all the compounds were carried out by the combination of DSC, POM and X-ray analysis. The effects of the various terminal normal/branched/ saturated/unsaturated alkyl chains and the position of the substituted fluorine atom with its structurally related compounds have been discussed.

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Effects of chain branching and chirality on liquid crystalline phases of bent-core molecules: blue phases, de Vries transitions and switching of diastereomeric states

Cited by 70 publications

References 80 publications

Unusual Electro‐Optic Kerr Response in a Self‐Stabilized Amorphous Blue Phase with Nanoscale Smectic Clusters

Unusual Electro‐Optic Kerr Response in a Self‐Stabilized Amorphous Blue Phase with Nanoscale Smectic Clusters

Polar Order and Symmetry Breaking at the Boundary between Bent‐Core and Rodlike Molecular Forms: When 4‐Cyanoresorcinol Meets the Carbosilane End Group

Effects of chain branching and lateral fluorine substitution on mesomorphism of cholesteryl benzoates

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